Drive-in speaker installation

ABSTRACT

In a sound system for drive-in theatres, speakers are connected in parallel to a common sound signal source in a junction head on a center support post between adjacent automobile spaces. A volume control for each speaker includes a limit stop on the volume control knob to assure that at least a limited amount of resistance is in the loudspeaker circuit so that when the speaker circuit is shunted by replacing it on the post to cut off the sound, it will not cut off the sound to the other speaker in use. Also, a high strength cable is associated with the connecting wires between each speaker and the junction head to prevent accidental or intentional removal or separation of the speaker from its support post.

United States Patent 1 Reed Sept. 17, 1974 DRIVE-IN SPEAKER INSTALLATION [76] Inventor: Samuel M. Reed, 2121 Routt,

Lakewood, Colo. 80215 22 Filed: Mar. 14, 1972 21 Appl. No.: 234,609

[52] US. Cl. 179/1 DD [51] Int. Cl H04r 27/00 [58] Field of Search 179/1 DD; 338/149 [56] References Cited UNITED STATES PATENTS 3,195,092 7/1965 Tumbusch 338/149 3,270,267 8/1966 Nolte, Jr. 179/1 DD 3,366,910 1/1968 Bush i 338/149 3,484,552 12/1969 Wells 179/1 DD Primary Examiner-Kathleen H. Claffy Assistant ExaminerDouglas W. Olms [5 7 ABSTRACT In a sound system for drive-in theatres, speakers are i connected in parallel to a common sound signal source in a junction head on a center support post between adjacent automobile spaces. A volume control I for each speaker includes a limit stop on the volume control knob to assure that at least a limited amount of resistance is in the loudspeaker circuit so that when the speaker circuit is shunted by replacing it on the post to cut off the sound, it will not cut off the sound to the other speaker in use. Also, a high strength cable is associated with the connecting wires between each speaker and the junction head to prevent accidental or intentional removal or separation of the speaker from its support post.

4 Claims, 6 Drawing Figures DRWE-IN SPEAKER INSTALLATION BACKGROUND OF THE INVENTION This invention generally relates to speaker systems and more specifically to drive-in speaker systems in which a pair of speakers are mounted on a common support post and receive sound signals through a junction head on the support post.

In speaker systems of the type described, conventionally underground wiring from the projection room am.- plifier system transmits sound signals through a set of connecting wires or leads internally through the common support post into a junction box or head located on the post. A pair of speakers are mounted on each post with electrical cords running from each speaker into the junction head for connection in parallel through a step-down transformer to the branched connecting leads from the sound system. Customarily, in each speaker system, the loudspeaker circuit is so constructed that when removed from the support post and placed on the automobile, usually by suspension from the window, the volume of the loudspeaker can be regulated through a volume control knob on the exterior of the housing. However, when the speaker is replaced on the support post the loudspeaker circuit will be shorted out to cut off the sound; and, if the speaker is replaced with the volume control at the maximum volume level, the resistance of the potentiometer is so negligible as to effectively short out the loudspeaker circuit in the other speaker. In the past, current limiting resistors have been employed to prevent shorting of one speaker when the other speaker is replaced and, for e xample, reference is made to US. Pat. No. to Orville C. Wells, 3,484,552 for a system of this type. While the circuitry disclosed therein is generally effective to minimize the danger of shorting of adjacent speakers, the circuitry does require modification of existing circuitry and the use of additional resistors in the circuit.

SUMMARY OF THE INVENTION It is therefore proposed to provide for an effective means of maintaining minimum resistance in the loudspeaker circuit when it is replaced on the supporting post without modifying existing circuitry or requiring the use of special resistors and is therefore readily conformable for use either as a permanent part of a speaker installation or for modification of existing speaker installations. It is further proposed to provide for a theft resistant connector between each speaker and the supporting post, to prevent accidental or intentional removal or separation of the speaker from the support post, wherein a high strength connector cable is anchored to the speaker housing and insulated from the housing in such a way as not to affectthe sound system.

It is therefore an object of the present invention to provide for a novel and improved speaker system which is particularly adaptable for use in drive-in theatres.

It is another object of the present invention to provide for a novel and effective means of providing minimum resistance in the loudspeaker circuit at all times to prevent shorting of another loudspeakercircuit in use in a simple and highly dependable manner.

It is a further objectof the present invention to provide for a theft-resistant cord or cable adapted for interconnection of each speaker housing to a supporting post in a drive-in speaker installation.

It is an additional object of the present invention to provide for a novel and improved speaker system which is highly efficient and dependable in use and incorporates an approved volume control knob protection circuit which will prevent shorting of other speaker systems in use when the speaker is replaced on its supporting post in a drive-in speaker installation.

In accordance with the present invention, there has been devised a drive-in speaker installation in which a pair of speaker units are electrically connected in parallel to the main connecting leads from a sound system into a junction head. Each speaker includes a housing with a mounting bracket adapted to be suspended from the junction head or from an automobile, such as, from the car window. Conventionally, each speaker includes a loudspeaker and voice coil mounted therein together with a potentiometer which is provided with a volume control resistor and movable control arm coupled to a control shaft in the housing to regulate the volume of each loudspeaker, and each loudspeaker circuit is shorted out to turn off the sound when the speaker is replaced on the junction head. The particular feature of the present invention resides in a volume control knob which is keyed to the control shaft for the movable control arm, the control knob preferably being located on the exterior of the housing to advance the control arm across the resistor'whereby to regulate the volume level of the loudspeaker circuit. In order to limit the maximum volume level so as to provide for minimum resistance in the circuit :at all times, a stationary abutment on the housing is engaged by a movable stop on the volume control knob to limit the extent of movement of the volume control arm to a point short of the end of the resistor so that a minimum resistance level is produced even at the maximum volume point established. As a result, the other speaker will not be shorted out when the one speaker unit is replaced on the junction head and left at its maximum volume level. Additionally, the connecting wires from the junction head to each speaker system are encased in a common sheath together with a high strength cable which is anchored in insulated relation to the speaker housing and to the loudspeaker circuit so as not to ground it out.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, advantages and features of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the preferred form of the present invention when taken together with the accompanying drawings, in which:

FIG. 1 is a somewhat prospective view of a typical drive-in speaker installation in accordance with the present invention.

FIG. 2 is a schematic illustration of the loudspeaker circuitry, junction head and connecting cable between one of the speakers and junction head in a speaker installation.

FIG. 3 is a somewhat fragmentary view, enlarged, of

the exterior of the speaker housing, and particularly of .the control knob section.

FIG. 4 is an elevational view of the inner surface of the control knob.

FIG. 5 is an elevational view, with a portion of the control .knob broken away to illustrate the relative disposition and arrangement between the control knob and volume control abutment on the speaker housing; and

FIG. 6 is a cross-sectional view in detail of the volume control knob, volume control stop and control shaft of the speaker housing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to detail to the drawings, there is shown by way of illustrative example in FIG. 1 a representative form of speaker installation generally designated at 10 and which is specifically designed and adapted for use in drive-in theatres. As illustrated, the speaker installation includes a center support post 12, a junction head cover 14 for a junction head which is stationed therein, diametrically opposed mounting brackets 15 on the housing 14 for suspension of generally rectangular speaker housings 18, each of the latter being equipped with a hanger bracket or arm 19 in a conventional manner. In drive-in theatres, a speaker installation as described is stationed between adjacent parking spaces with a speaker provided for each car. Moreover, in the usual manner, underground wiring from a projection room amplifier system has conducting wires 21 and 22, as represented in FIG. 2, extending internally through each post for connection to the primary side of a transformer 23 in the junction head 13. A ground connection 24 is made on the secondary side of the transformer 23, and the secondary is connected in parallel to conducting wires 25 and 26 which lead away from the junction head to each of the speaker systems. Preferably the conducting wires 25 and 26 extend through an outer sheath 27, together with a high strength connector cable 28, one end of the cable 28 being anchored as at 29 to the junction head housing by a suitable dowel pin, and the other end of the cable 28 being anchored by an insulated dowel pin 31 to the speaker housing. Connection of the conducting wires in this manner will minimize theft or removal of the speaker from the supporting post, for example, which may otherwise occur if a customer should drive off and inadvertently forget to replace a speaker on the junction head. At the same time, the insulated connection of the cable to the speaker housing will prevent shorting out or grounding of the speaker system through the high strength cable.

The components and circuitry of each speaker system are identical and accordingly only a single speaker system is shown and described. In each speaker, leads 25 and 26 are connected to terminals 32 and 33, respectively, at opposite ends of resistor 34 of a potentiometer. The potentiometer also includes a movable control arm 35 which is coupled to a control shaft represented at 36 for movement across the resistor 34 to select the desired resistance setting and resultant volume of the loudspeaker circuit. A connecting lead 38 extends from the terminal end of the control arm 35 attached to the control shaft to terminal 39 for a ground wire 40 and, although not shown, the ground wire 40 leads from the loudspeaker circuit for connection to the speaker housing 18. A loudspeaker is represented at 42 which is provided with a voice coil 43, one side of which is connected through connecting lead 44 to the terminal 32 for conducting wire 25, and the opposite side 45 is connected to terminal 39 for the ground lead 40.

An important feature of the present invention resides in a protection system which is designed to reduce the maximum volume level of the loudspeaker circuit, but most particularly is intended to prevent shutoff or shorting of one speaker when another speaker is replaced on a mounting bracket 15 on the junction head with the control knob left at its maximum volume level. In other words, the control knob is so designed as to assure some minimum resistance in the resistor 34 when the rest of the loudspeaker circuit is shunted upon replacement of the speaker on the mounting bracket; otherwise, in the absence of any resistance which would result if the control arm could be advanced beyond the end of the resistor 34 at or adjacent to the terminal 33, the loudspeaker circuit for the other speaker system would be cut off as well. In order to avoid this occurrence, and as shown in FIGS. 3 to 6, an abutment or limit stop projects from the external surface of the speaker housing 18 directly below the control shaft 36. In accordance with conventional practice, the control shaft 36 has a flatted end surface 36 to permit it to be keyed for rotation with the volume control knob. As illustrated in FIGS. 4 to 6, a volume control knob 52 is of generally circular configuration and is provided with a central opening 56 and a flattened surface 56' so as to correspond to the cross sectional size and configuration of the control shaft for snugfitting engagement therewith. Of course, when the control knob 52 is placed on the control shaft, it will permit regulation of the volume control arm 35 in the potentiometer to regulate the volume level of the loudspeaker circuit in the usual manner. However, in order to limit the maximum volume level and assure a minimum resistance in the resistor 34 at all times, a circular channel or groove 58 is formed in the inner surface of the control knob at a radial distance from the center opening equal to the distance of the abutment 50 from the axis of the control shaft 36 so that the channel 58 will be aligned to receive the abutment 50 therein. However, a limited portion of the channel is interrupted by a rotation stop 59 which is engagable with the abutment on limit stop 50 to limit movement of the control arm toward the one terminal 33 of the resistor 34, as represented also in FIG. 2. In order to assure proper installation of the knob on the volume control shaft, the volume control shaft should be turned to the extreme right then backed off to the left about one-quarter turn before the knob is installed. The knob is then placed on the control shaft with the abutment 50 projecting into the channel 58 as described.

It will be evident from the foregoing that the abutmentor stud 50 may either be cast in the exterior of the housing or simply may be inserted in a hole drilled or otherwise formed in a conventional speaker housing, and the special control knob is placed over the control shaft in proper alignment with the abutment 50 to assure desired volume control of the loudspeaker circuit. Accordingly, the volume control limit stop arrangement as described is readily conformable for use with other speaker systems as well as the specific one described.

In use, the speaker units are normally mounted on the junction head mounting brackets 15 and the voice coils 43 will be shunted through the ground connection 40 and speakerhousing 18 into the junction head 13 so that the loudspeaker circuits are bypassed and current will flow only through the resistors 34. However, when the speaker unit is removed from the mounting bracket and placed on an automobile, the volume control level is suitably regulated by rotation of the volume control knob to advance the control arm 35 across the resistor 34 in a conventional manner. Again, assuming that the control knob is left at the full volume level when the speaker is replaced on the junction head mounting bracket, the cooperating limit stops 50 and 59 will assure some minimum resistance in the resistors 34 to prevent shorting out or cutoff of the other speaker system when the other speaker system is in use.

Most desirably, the cable 28 is a high strength steel aircraft cable, for example, a 1,000 pound strain cable in order to securely anchor the speaker system to the junction head and prevent theft or inadvertent removal.

It is therefore to be understood from the foregoing that while a preferred form of the present invention has been set forth and described herein, various modifications and changes may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In a drive-in speaker system wherein a pair of speaker units are electrically connected in parallel to electrical leads extending from a sound-generating source into a junction head, each speaker including a housing with a mounting arm adapted to be suspended from the junction head and removable therefrom for suspension from an automobile, a loudspeaker and voice coil mounted in each housing together with a potentiometer which is provided with a volume control resistor connected across the electrical leads and movable control arm electrically connected directly to the loudspeaker and coupled to a control shaft in the housing to regulate the volume of the loudspeaker, each said voice coil being shunted to turn off the sound when the respective speaker is mounted on the junction head, the improvement comprising:

a volume control knob keyed to the control shaft externally of said housing, said volume control knob being accessible for rotation from the exterior of said housing to advance the volume control arm in the potentiometer across its resistor whereby to regulate the volume level; and

a stationary abutment mounted on the exterior of the housing and movable stop means enclosed by said volume control knob and rotatable with said volume control knob to engage said abutment whereby to limit the movement of said volume control arm to a point short of negligible resistance on the potentiometer so that a minimum predetermined resistance level is produced at the maximum volume established in order to prevent one speaker unit from shorting out the other speaker unit when the one speaker unit is mounted on the junction head and left at its maximum volume level.

2. In a drive-in speaker system according to claim 1, said abutment projecting outwardly from the external surface of the speaker housing in spaced relation to the control shaft, and said control knob including a circular channel on its inner surface aligned to receive said abutment, and said movable stop means being located in said channel at a position to contact said abutment whereby to limit movement of the control arm to a point short of the maximum volume level.

3. In a drive-in speaker system according to claim 2, said abutment and stop being so disposed as to maintain a minimum of l to 2 ohms resistance in the loudspeaker circuit when the potentiometer is at its maximum volume level.

4. In a drive-in speaker system according to claim 1, wherein an electrical cord interconnects each speaker circuit to the junction head, said cord enclosing a pair of conducting leads and a high strength connector cable, said connector cable anchored at opposite ends to said junction head and speaker housing, respectively, at least one end of said cable being connected by an insulator to one of said speaker housing and junction head to prevent grounding of said cord to the speaker housing. 

1. In a drive-in speaker system wherein a pair of speaker units are electrically connected in parallel to electrical leads extending from a sound-generating source into a junction head, each speaker including a housing with a mounting arm adapted to be suspended from the junction head and removable thErefrom for suspension from an automobile, a loudspeaker and voice coil mounted in each housing together with a potentiometer which is provided with a volume control resistor connected across the electrical leads and movable control arm electrically connected directly to the loudspeaker and coupled to a control shaft in the housing to regulate the volume of the loudspeaker, each said voice coil being shunted to turn off the sound when the respective speaker is mounted on the junction head, the improvement comprising: a volume control knob keyed to the control shaft externally of said housing, said volume control knob being accessible for rotation from the exterior of said housing to advance the volume control arm in the potentiometer across its resistor whereby to regulate the volume level; and a stationary abutment mounted on the exterior of the housing and movable stop means enclosed by said volume control knob and rotatable with said volume control knob to engage said abutment whereby to limit the movement of said volume control arm to a point short of negligible resistance on the potentiometer so that a minimum predetermined resistance level is produced at the maximum volume established in order to prevent one speaker unit from shorting out the other speaker unit when the one speaker unit is mounted on the junction head and left at its maximum volume level.
 2. In a drive-in speaker system according to claim 1, said abutment projecting outwardly from the external surface of the speaker housing in spaced relation to the control shaft, and said control knob including a circular channel on its inner surface aligned to receive said abutment, and said movable stop means being located in said channel at a position to contact said abutment whereby to limit movement of the control arm to a point short of the maximum volume level.
 3. In a drive-in speaker system according to claim 2, said abutment and stop being so disposed as to maintain a minimum of 1 to 2 ohms resistance in the loudspeaker circuit when the potentiometer is at its maximum volume level.
 4. In a drive-in speaker system according to claim 1, wherein an electrical cord interconnects each speaker circuit to the junction head, said cord enclosing a pair of conducting leads and a high strength connector cable, said connector cable anchored at opposite ends to said junction head and speaker housing, respectively, at least one end of said cable being connected by an insulator to one of said speaker housing and junction head to prevent grounding of said cord to the speaker housing. 